Pub. Util. Code, § 12751

(a) Except as specified in Section 12751.5, the purchase of all supplies and materials, when the expenditure required exceeds twenty-five thousand dollars ($25,000), or in a district that has a population of 250,000 or more, when the expenditure required exceeds fifty thousand dollars ($50,000), shall be by contract let to the lowest responsible bidder. Notice requesting bids shall be published pursuant to Section 6061 of the Government Code at least 10 days before bids are received. The district may reject any and all bids and readvertise in its discretion. The board may authorize the general manager to determine, in the discretion of the general manager, whether to reject all bids and whether, after the bids have been rejected, to readvertise.

(b) The dollar limit identified in subdivision (a) shall annually be adjusted upward or downward to reflect the percentage change in the Implicit Price Deflator for State and Local Government Purchases of Goods and Services for the United States, as published by the U.S. Department of Commerce. The annual adjustments shall be rounded to the nearest one thousand dollars ($1,000).